1. Field of the invention:
This invention relates to a V belt for high load transmitting, comprising endless load carriers and a plurality of blocks to be engaged with each of said load carriers.
The V belt according to the present invention is usable not only as the V belt of a continuously variable transmission for motor vehicles but also as the V belt of a continuous variable or uncontinuously variable transmission for vehicles loaded with engines, such as agricultural machines and civil engineering machines. It is also suitable for a V belt for high load for general industrial machines to be driven by electric motors.
2. Description of the prior art:
For a transmission for running of a motor vehicle, a combine, a tractor or the like, a gear type transmission or an oil pressure type transmission is used. However, for the purposes of improving workability, saving fuel expenses, etc., development of a belt type continuously variable transmission is in progress.
The belt is to be used for this belt type continuously variable transmission is required to have high torque transmitting ability, but the conventional rubber V belt is not useful for such belt type continuously variable transmission because it cannot stand high lateral pressure, namely, it buckles and deforms by high lateral pressure.
Various types of transmission for high load transmitting have been suggested up to now (for example, Japanese Patent Application Laying Open Gazettes Nos. 46-4861, 55-27595, 56-76745, 59-77147 and 61-206847). The applicants themselves have suggested the V belt of such construction that a plurality of blocks are engaged with an endless load carrier in the lengthwise direction of belt (U.S. Pat. No. 4,655,732 corresponding to Japanese Patent Application Laying Open Gazette No. 60-49151). The applicants have also filed patent applications for V belt of similar type (U.S. patent applications Nos. 903,346, now U.S. Pat. No. 4,734,085 and 34,461).
The conventional block for such V belt is so shaped that it is gradually small in shape toward the lower part (in the case where it is composed of material of the same specific gravity) and therefore its center of gravity is usually located at the upper side of the tensile member. In the case where reinforcing members or the like of different specific gravity are embedded within, the location of the center of gravity varies with the reinforcing members or the like. Thus, no consideration has been given to the location of the center of gravity of the block.
Blocks whose center of gravity is biassed below the tensile member (toward the center of pulley) have been disclosed, for example, by Japanese Utility Model Registration Application Laying Open Gazettes Nos. pb 60-177351, 60-101246, 61-73940 and U.S. Pat. No. 4,595,385. Blocks whose center of gravity is biassed above the tensile member are disclosed, for example, by Japanese Patent Application Gazettes Nos. 57-79347 and 57-28815.
A pulley on which such V belt is wound comprises movable sheaves and fixed sheaves, both of truncated cone shape of the same angle. As shown in FIG. 17(a) and FIG. 17(b), it is so designed that when the block 101 engaged with the load carrier advances into a pulley groove of a pulley 102 and engages with pulley groove surfaces 102a, 102b, no gap is left between side surfaces 101a, 101b of the block 101 and the pulley groove surfaces 102a, 102b, in the case where the block 101 stands perpendicularly in relation to the load carrier (namely, in the case where the center line S of the block 101 coincides with the radial direction R of the pulley 102). (Please refer to FIG. 17(b)). W designates the center line of the tensile member of load carrier.
In the V belt as stated above, as shown by FIG. 18(a), when the block 101 engages with groove surfaces 102a, 102b of the pulley 102, if the upper part of the block 101 inclines to the T side in the rotational direction of the pulley, groove surfaces 102a, 102b of the pulley 102 take the shape of a hyperbolic curve, in the cross section at the center line, and also form the pulley angle which is smaller than the angle formed by both side surfaces 101a, 101b of the block 101 and therefore only the upper end portion of the block 101 makes contact with pulley groove surfaces 102a, 102b (refer to FIG. 18(b)). Therefore, when the block 101 engages with groove surfaces 102a, 102b of the pulley 102, rocking of the block 101 is caused, with P.sub.1 (the upper end portion of the block 101 at which the block 101 and pulley groove surfaces 102a, 102b make contact with each other) as a fulcrum and the groove in which the load carrier is fitted as a working point. This is proved by the following fact.
If comparison is made between the case where the point a is given at the position above the groove 101c in which the load carrier of the block 101 is fitted and the center line of the block 101 coincides with the radial direction R of the pulley 102 with the point a fixed on pulley groove surfaces 102a, 102b (refer to chain lines in FIG. 19) and the case where the center of the block 101 inclines at an angle .theta. to the radial direction R, it is found out that in the case of the latter (the block 101 inclines at an angle .theta. to the pulley radial direction R) the groove 101c of the block 101 in which the load carrier is fitted is situated more away from the center 0 of pulley rotation and accordingly the block 101 is moved to the position where it stands perpendicularly on the pulley due to pressing force F of the load carrier wound on the pulley 102 to the rotational center 0 of the pulley.
On the contrary, as shown by FIG. 20(a), if the lower part of the block 101 inclines to T side in pulley rotational direction when the block 101 engages with pulley groove surfaces 102a, 102b of the pulley 102, the cross section at the center line of the block indicates that as shown by FIG. 20(b), the pulley groove surfaces 102a, 102b take the shape of a hyperbolic curve and also form a small pulley angle in relation to the block angle. Therefore, similarly to the above-mentioned case, when the block 101 engages with pulley groove surfaces of the pulley 102, only the upper end portion of the block makes contact with the pulley groove surfaces 102a, 120b and rocking of the block 101 is caused, with the contact part P.sub.2 as a fulcrum point and the groove in which the load carrier is fitted as a working point.
As mentioned above, in the case where the block 101 inclines to the pulley radial direction when the block engages with the pulley 102, rocking of the block 101 is caused and accordingly friction is generated at the part where the block 101 engages with the load carrier and this friction involves the generation of heat and resultant partial temperature rise of the block and the load carrier. This naturally causes ageing due to heat on rubber composing the load carrier. Thus, the load carrier cracks and if cracks reach the tensile member, earlier breakage of the load carrier occurs.
As stated above, if the block inclines to the pulley radial direction when the block engages with the pulley, only the upper end portion of the block makes contact with the pulley groove surfaces of the pulley. This means that the lateral pressure which should be received by the whole of the block side surface concentrates upon the upper end portion of the block, causing chipping and early damage of blocks. It is therefore necessary to engage the block with the pulley, with the block coinciding with the pulley radial direction.